NYSCTU Stream Assessment Manual Glossary
Adapted from Craig Fischenich, February 2000,
USAE Research & Development Center, Environmental Lab,
3909 Halls Ferry Rd, Vicksburg, MS 39180
& ERDC TN-EMRRP-SR-01 1 Glossary of Stream Restoration Terms
(this adaptation by John Braico, NYS Council TU Resource Management VP)
Adjustment Process – or type of change underway due to natural causes or human activity that has or will result in a change to the valley, floodplain & or channel condition
(i.e. vertical, lateral, or channel planform adjustment processes)
Aggredation
– A progressive buildup or raising of the channel bed and floodplain due to sediment desposition. The geologic process by which streambeds are raised in elevation and floodplains are formed. Aggredation indicates that stream discharge and or bedload characteristics are changing. Opposite of degredation.
Alluvial – deposited by running water
Alluvium – a general term for detrital deposits (often silty or silty clay) made by streams on riverbeds, floodplains & alluvial fans. The term applies to stream deposits of recent time, not subaqueous sediments.
Armoring – a natural process where an erosion resistant layer of relatively large particles is established on the surface of the streambed through removal of finer particles by stream flow. A properly armored streambed generally resists movement of bed material at discharges up to roughly ¾ bankfull depth.
Avulsion
—a change in channel course that occurs when a stream suddenly breasks through its banks, typically bisecting an overextended meander arc.
Backwater – a small generally shallow body of water attached to the main channel with little or now current of its own.
Backwater pool – pool formed as a result of an obstruction (weir, dam, boulder, tree)
Bank stability
– the ability of a streambank to counteract erosion or gravity forces.
Bankfull channel depth – 1) the maximum depth of a channel within a riffle segment when flowing at a bankfull discharge (Dmax). 2) The mean depth of such a riffle segment under such conditions (Dmean).
Bankfull channel width – the surface width of a stream channel when flowing at a bankfull discharge as measured between banks.
Bankfull discharge – the stream discharge corresponding to the water stage that just starts to flow onto the active flood plain.
Bankfull indicators – physical findings adjacent to the active channel reflective of the edge of the active flood plain, e.g. top of a point bar, a topographic break in slope, a shift in size distribution of surface materials (Leopold).
Bar – an accumulation of alluvium (typically gravel or sand) caused by decrease in sediment transport capacity on the inside of meander bends or in the center of an over wide channel.
Barrier – a physical block or impediment to the movement or migration of fish – such as a waterfall (natural barrier) or a dam (man made barrier).
Base flow – the sustained portion of stream discharge that is drawn from natural ground water storage sources & reflects the water table’s elevation.
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Bedload
– sediment moving on or near the streambed and transported by jumping, rolling or sliding on the bed layer of a stream.
Bed material – the sediment mixture that comprises a streambed
Bed material load – that portion of the total sediment load with sediments of a size found in the streambed.
Bed roughness – a measure of the irregularity of the streambed as it contributes to flow resistance. Commonly expressed as a Manning “n” value.
Bed slope – the inclination of the channel bottom, measured as the elevation drop er unit length of the channel.
Bethentic invertebrates –Aquatic animals without backbones that dwell on or in the bottom sediments of water.
Berms
– mounds of earth, gravel or other fill built parallel to the stream banks and designed to keep flood flows from entering the adjacent flood plain.
Biota – all living organisms of a region, as in a stream or other body of water.
Boulder
– rock larger than cobble measuring 256 mm
Braided channel – a stream characterized by flow within several channels, which successively meet & divide. Braiding often occurs when sediment loading is too great to be carried by a single channel.
Braiding of river channels – successive division and rejoining of river flow with accompanying islands.
Buffer strip – a barrier of permanent vegetation, either forest or other, between waterways and land uses such as agriculture or urban development, designed to intercept and filter out pollution before it reaches the stream.
Canopy
– a layer of foliage in a forest that provide shade & cover for fish & wildlife
Cascade
– a short, steep drop in streambed elevation often marked by boulders and white water.
Channel
– an area that contains continuously or periodically flowing water that is confined by banks and a streambed.
Channelization
– the process of changing the natural path of a waterway (usually straightening)
Coarse woody debris (CWD) – portion of a tree that has fallen or been cut and left in the woods. (Usually pieces at least 20” in diameter)
Cobble – particles that are smaller than boulders and larger than gravels, i.e., ranging between 64-256mm.
Cover
– a general term to describe any structure that provides refugia for fish, reptiles or amphibians. (size may range from cobbles to boulders, include undercut banks, snags, submerged logs)
Critical shear stress – the minimum amount of shear stress exerted by stream currents required to initiate particle motion. (This stress is less for banks than for stream beds due to the added effect of gravity for banks).
Degredation – 1) A progressive lowering of the channel bed due to scour. Degradation is often an indicator that the stream’s discharge is increasing and/or sediment load is lessening. It may also be initiated by an activity that locally disrupts bed armor & increases bed scour as may be seen with culverts.
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Detritus – organic material, such as leaves, twigs & other dead plant material that collects on the stream bottom. It may occur in clumps as in leaf packs on the bottom of a pool or as single pieces such as a fallen tree branch.
Dissolved Oxygen (DO) – the amount of free oxygen dissolved in water expressed as milligrams/liter, parts per million, or % saturation.
Drainage area – The total surface area upstream of a point on a stream that drains toward that point. Note that this is distinct from a watershed & that the drainage area may contain one or more watersheds.
Embeddedness
– a measure of the amount of surface area of cobbles, boulders, snags & other stream bottom structures that is covered with sand and silt. An embedded streambed may be packed hard with sand and silt such that rocks in the stream bottom are difficult or impossible to pick up. The spaces between the rocks are filled with fine sediments, leaving little room for fish, amphibians & bugs to use the structures for cover, resting, spawning and feeding. A streambed that is NOT imbedded has lose rocks that are easily removed from the stream bottom, and may even roll on one another when walked upon.
Entrenchement ratio – the width of the flood prone area divided by the bankfull width.
Ephemeral streams – streams that flow only in direct response to precipitation and who channel is at all times above the water table.
Eutrophication – the process of enrichment of water bodies by nutrients
Floodplain
– land being continuously built & rebuilt of alluvial sediments & that continues to be regularly covered with water as a result of the flooding of a nearby stream
Flow – the amount of water passing a particular point in a stream usually expressed in cubic feet per second.
Fluvial
– of or pertaining to streams or rivers
Gaging station – a particular site on a stream where hydrologic data are obtained
Geomorphology – a branch of both physiography and geology dealing with the form of the earth, the general configuration of its surface, and the changes that take place due to erosion of the primary elements and the buildup of erosional debris.
Glide – a shallow section of stream that has little or no turbulence
Gradient – vertical drop per unit of horizontal distance
Gravel – an unconsolidated accumulation of rounded rock fragments, mostly of particles larger than sand (> 2mm) & less than boulders (< 256mm).
Ground water table – the upper surface of the zone of saturation, except where the surface is formed by an impermeable layer.
Habitat diversity – the number of different types of habitat within a given area.
High gradient streams – typically steep cascades, step/pool streams, or streams that exhibit riffle/pool sequences.
Hydraulic gradient – the slope of the water surface.
Hydraulic radius – the cross sectional area of a stream divided by the wetted perimeter
Hydrograph – a curve showing stream discharge over time
Hydrologic balance – an accounting of all water inflow into, outflow from & changes in water storage within a hydrologic unit over a specified period of time.
Hydrologic region – a study area consisting of one or more planning subareas that has a common hydrologic character.
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Hydrology – the scientific study of the water of the earth, its occurrence, circulation and distribution, its chemical and physical properties and its interaction with its environment, including its relationship to living things.
Hyporheic zone – the area under the stream channel and flood plain where groundwater and the surface waters of the stream are exchanged freely.
Incised stream – a river that erodes its channel by the process of degradation to a lower base level than existed previously or is consistent with the current hydrology.
Incision ratio – a quantitative measure of channel incision expressed as low bank height divided by maximum channel depth.
Infiltration
– the movement of water through the soil surface into the soil.
Intermittent stream – any nonpermanent flowing drainage feature having a definable channel and evidence of scour or deposition.
Large woody debris (LWD) -- pieces of wood larger than 10 ft long and 6” in diameter in a stream channel.
Levee
– an embankment constructed to prevent a stream from flooding
Limiting factor – a requirement such as food, cover, or another physical, chemical or biological factor that is in shortest supply with respect to all the resources necessary to sustain a life form & thus “limits” the size or retards production of a population.
Low gradient stream – streams that typically appear slow moving and meandering, have less clearly defined riffles and pools. Typically found in large valleys, wetlands & some meadows.
Macroinvertebrates
– invertebrates visible to the naked eye such as insect larvae & crayfish
Macrophytes – aquatic plants large enough to be seen with the naked eye
Mass movement – the downslope movement of earth caused by gravity. Includes but is not limited to landslides, rock falls, debris avalanches & creep. It does not include surface erosion by running water. It may be caused by natural erosional processes, by natural disturbances, or by human disturbances.
Mean annual discharge – daily mean discharge averaged over a period of years. Mean annual discharge generally fills a channel to about 1/3 of its bankfull discharge.
Mean velocity – The average cross sectional velocity of water in a stream channel.
Meander – The winding of a stream channel in an erodible alluvial valley. A series of sine generated curves characterized by curved flow and alternating banks and shoals.
Meander belt width – the distance between lines drawn tangential to the extreme limits of fully developed meanders.
Meander Amplitude – the distance between points of maximum curvature of successive meanders of opposite phase in a direction normal to the general course of the meander belt, measured between center lines of channels.
Meander length – the lineal distance down valley between two corresponding points of successive meanders of the same phase.
Mid-channel bars – bars located in the channel away from the banks, generally found in areas where the channel runs straight. Mid channel bars are caused by recent channel instability and are unvegetated.
Perennial streams – those that flow continuously pH
– the negative logarithm of the molar concentration of the hydrogen ion, or more simply, the scale used to measure acids & bases. 1.0 = maximal acidity, 7.0 = neutral.
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Point bar – the convex side of a meander bend that is built up due to sediment deposition.
Pool – a reach of stream characterized by deep low velocity water with a smooth surface.
Pool/riffle ratio – the ratio of surface area or length of pools to the surface area or length of riffles in a given stream reach.
Rapids – a reach of stream characterized by small falls and turbulent high velocity water
Reach
– a section of stream having relatively uniform physical attributes, such as valley confinement, slope, sinuosity, dominant bed material & bed form.
Rearing habitat – areas in streams where juvenile fish find food and shelter.
Regime theory – A theory of channel formation that applies to streams that make a part of their boundaries from their transported sediment load and a portion of their transported sediment load from their boundaries. Channels are considered “in regime” or equilibrium when bank erosion and bank formation are equal.
Restoration – The return of an ecosystem to a close approximation of its condition prior to disturbance
Riffle – a stream reach characterized by shallow, fast moving water broken by the presence of rocks & boulders.
Riffle/step frequency – ratio of the distance between riffles to the stream width.
Riparian buffer – the width of naturally vegetated land adjacent to the stream between the top of the bank (or top of slope, depending upon site characteristics) & the edge of other land uses. A buffer is largely undisturbed and consists of trees, shrubs, ground cover plants, duff layer & naturally uneven ground surface. The buffer serves to protect the water body from the impacts of adjacent land uses.
Riparian corridor – includes lands defined by the lateral extent of a streams meanders necessary to maintain a stable stream dimension, pattern, profile & sediment regime. For instance, in a stable pool-riffle stream system, riparian corridors may be as wide as 10-12 times the channel bankfull width. In addition the riparian corridor typically corresponds to the land area surrounding and including the stream that supports a distinct ecosystem, generally with abundant and diverse plant and animal communities.
Riparian habitat – the aquatic and terrestrial habitat adjacent to streams.
Riparian
– located on the banks of a stream.
Riparian vegetation – the plants that grow adjacent to a stream and that relyupon the hydrology of the associated water body.
River stage – the elevation of the water surface at a specified station above some arbitrary zero level (or datum).
Rootwad
– the exposed mass of roots associated with a tree adjacent to or in a stram that provides refuge for fish & or other aquatic life. A device developed by Dave Rosgen utilizing a large exposed root fan with the tree trunk anchored & buried securely into the bank.
Run – A reach of stream characterized by fast flowing, low turbulence water
Runoff
– water that flows over the ground and reaches a stream as a result of rainfall or snowmelt.
Scour – the erosive action of running water in streams, which excavates & carries away material from the bed and banks. Scour may occur in both earth and solid rock material and can be classed as general, contraction or local scour.
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Sediment – soil or mineral material transported by water or wind & deposited bin streams.
Sedimentation – 1) The combined processes of soil erosion, entrainment, transport, deposition and consolidation. 2) Deposition of sediment.
Segment
– a relatively homogenous section of stream contained within a reach that has the same reference stream characteristics but is distinct from other segments in the reach in one or more of the following parameters: degree of flood plain encroachment, presence/absence of grade controls, bankfull channel dimensions (W/D ration, entrenchment), channel sinuosity & slope, riparian buffer & corridor conditions, abundance of springs/seeps/adjacent wetlands/storm water inputs & degree of channel alteration.
Sensitivity
– of the valley, flood plain & or channel condition to change due to natural causes & or anticipated human activity.
Siltation – the deposition or accumulation of fine soil particles.
Sinuosity – the ratio of the channel length to direct down valley distance.
Slope – the ratio of the change in elevation over distance
Slope stability – the resistance of a natural or artificial slope to failure by mass movement.
Snag – any standing dead, partially dead or defective tree at least 10” in diameter at breast height and at least 6’ tall.
Stable channel – A stream channel with the right balance of slope, planform and cross section to transport both the water and sediment load without net long-term bed or bank sediment deposition or erosion throughout the stream segment.
Stream gradient – a general slope or rate of change in vertical elevation per unit of horizontal distance of the (1) bed, (2) water surface, or (3) energy grade of a stream.
Stream morphology – the form and structure of streams.
Stream order – a hydrologic system of stream classification. Each unbranched tributary is 1 st
order, two 1 st
order streams join to form a 2 nd
order & so forth.
Stream Reach – an individual segment of a stream that has beginning and ending points defined by identifiable features.
Stream type – gives the overall physical characteristics of the channel segment and helps predict the reference or stable condition of the reach. (See Rosgen Stream Types)
Stream bed – the unvegetated portion of a channel boundary below the base flow level.
2) The channel through which a natural stream of water runs or used to run.
Stream flow – The rate at which water passes a given point in a stream expressed in cubic feet per second (CFS).
Step – A steep step like feature in a high gradient stream (>2%). Steps are composed of large boulder lines across the stream.. Steps are important for providing grade-control, and for dissipating energy. As fast-shallow water flows over the steps it takes various flow paths thus dissipating energy during high flow events.
Substrate – 1) The composition of a stream bed including either mineral or organic materials. 2) Material that forms an attachment medium for organisms.
Surface erosion – The detachment and transport of soil particles by wind, water or gravity. Or a group or processes whereby soil materials are removed by running water.
Suspended sediment – sediment suspended in a fluid by the upward components of turbulent currents.
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Suspended sediment load – that portion of a streams total sediment load that is transported within the body of water and has very little contact with the stream bed.
Thalweg – 1) The lowest thread along the axial part of a valley or stream channel. 2)
The middle, chief or deepest part of a stream channel.
Tractive Force – the drag on a stream bed or bank caused by passing water that tends to pull particles along with the stream flow.
Turbidity – a measure of the content of suspended matter that interferes with the passage of light though the water or in which visual depth is restricted.
Urban run off – storm water from streets & gutters that usually carries a great deal of litter, bacterial wastes into receiving waters.
Water quality – a term used to describe the chemical, physical & biological characteristics of water, usually in respect to its suitability for a particular purpose.
Watershed – an area of land whose total surface drainage flows to a single point in a stream.
Watershed management – The analysis, protection, development, operation or maintenance of the land, vegetation, & water resources of a drainage basin for the conservation of all its resources for the benefit of its residents.
Watershed project – A comprehensive program of structural and non structural measures to preserve or restore a watershed to good hydrologic condition & reduce flood peaks & sediment production/transport.
Watershed restoration – Improving current conditions of watersheds to restore degraded habitat and provide long term protection to aquatic and riparian resources.
Weir – A structure to control water levels in a stream.. Depending upon the configuration, weirs can provide a specific “rating” for discharge as a function of the upstream water level.
Woody debris – referring to wood in streams.
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